1. Field of the Invention
This invention pertains to a new and improved process for preparing symmetrical tetrachloropyridine from pentachloropyridine. Tetrachloropyridine is an important commercial product which is used extensively in the preparation of insecticides.
2. Prior Art Description
Symmetrical tetrachloropyridine is prepared through a variety of processes. In a process as taught in Russian Pat. No. 539,034, an alkali dialkyl phosphite in N,N-dimethylformamide is added to 4-iodotetrachloropyridine, to form the desired symmetrical tetrachloropyridine. The reaction is carried out at temperatures from 140.degree. C. to 160.degree. C.
In U.S. Pat. No. 3,538,100, symmetrical tetrachloropyridine is prepared from the reaction of 2,6-dichloropyridine and chlorine in the presence of a catalyst. Pentachloropyridine is also produced as a contaminating by-product.
Another method for producing symmetrical tetrachloropyridine is by the reaction of pentachloropyridine with an oxidizable metal (e.g., Zn) in the presence of an acid (e.g., aqueous HCl). According to Dean et al. in U.S. Pat. No. 3,993,654, this reaction is run in an aqueous medium at a temperature of 110.degree. C. However, due to the cost and corrosive nature of the reaction mixture, other methods of preparation are desirable.